Ritual spells always require raw vis and a considerable amount of time. They require elaborate ceremonies that take into account factors such as astrological conditions, the mystical qualities of the target, and so on. The Abilities of Artes Liberales and Philosophiae help in the casting of ritual spells (in ArM5 only). Note, however, that the rules do not stipulate the need for any particular specific knowledge or materials (beyond raw vis); some troupes choose to assume, as a house rule, that the ritual casting requires use of appropriate mundane materials and instruments, that are assumed to be available - this is in accordance with the expanded rules given in Houses of Hermes: Societates regarding Ceremonial Casting.

Exact rules for casting ritual spells, including the amount of vis required. are found on page 81 of ArM5.